This invention relates generally to gas lasers and particularly relates to a gas laser having supersonic flow of the lasing gases and means for shifting the normal doppler bandwidth of the laser by a predetermined amount.
For various purposes it is desirable to provide a high energy laser having a large bandwidth. Such a bandwidth, for example, is useful for frequency modulation. For example, a chirp radar provides a signal where the frequency is swept over a certain frequency range. The received signal can then be compressed to generate a pulse having a small width in time, which technique is called pulse compression. The larger the bandwidth of the laser the greater the resulting compression and the more precisely the time of arrival of the pulse can be determined.
A laser having a large bandwidth can, therefore, be used as an optical radar which provides great range resolution. The range resolution is generally proportional to the compressed pulse length which in turn is inversely proportional to the bandwidth. Hence, the range resolution is inversely proportional to the bandwidth. This can, for example, be achieved by a laser of glass doped with neodymium. Such a laser has a very wide linewidth which permits to measure range within a fraction of a centimeter. Unfortunately, the neodymium doped lasers are not only very inefficient, but also have a low average power output.
On the other hand, chemical lasers are very efficient and have great average power capability. Hence, chemical lasers should be highly suitable for the purposes indicated above. However, the problem is that the bandwidths of all known chemical lasers are insufficient. By way of example, a DF laser has a bandwidth at full width half maximum of 350 mhz (megahertz) at an intensity of 1/e. An HF laser at the same intensity has a bandwidth of only about 250 mhz. On the other hand, for the purposes discussed the bandwidth needed is about 1.5 ghz.
It is, therefore, an object of the present invention to provide a gas laser having a bandwidth which substantially exceeds the normal doppler bandwidth.
A further object of the present invention is to adjust the bandwidth of a gas laser to the desired value in accordance with the flow velocity of the lasing gases.
Still a further object of the present invention is to provide a broadband gas laser of the type discussed where the gain profile, that is the gain as a function of frequency, can be tailored for any particular need.